Tiny toxic proteins help gut bacteria defeat rivals

Microcins
MĪ-kro-sins n.
Bacterial proteins that kill rival bacteria

Competition is cutthroat in the crowded world of the intestines, so bacteria have evolved ways to kill rivals for a survival advantage. One strain of bacteria, called Escherichia coli Nissle 1917, has tiny proteins called microcins that may help E. coli’s host fight pathogens that cause gut inflammation, researchers at the University of California, Irvine report online October 31 in Nature.

Microcins take action only when bacteria are starved for iron, which happens in an inflamed gut. The proteins go after bacteria, many of them pathogens, that make iron-scavenging proteins, the researchers found. E. coli Nissle’s microcins killed diarrhea-inducing bacteria called Salmonella enterica in the guts of infected mice. Microcins also helped Nissle outcompete a different, nasty strain of E. coli.